Integrated circuit heat dissipation using nanostructures

ABSTRACT

An approach for heat dissipation in integrated circuit devices is provided. A method includes forming an isolation layer on an electrically conductive feature of an integrated circuit device. The method also includes forming an electrically conductive layer on the isolation layer. The method additionally includes forming a plurality of nanowire structures on a surface of the electrically conductive layer

FIELD OF THE INVENTION

The present invention relates to integrated circuits and, moreparticularly, to methods and systems for dissipating heat in integratedcircuit devices.

BACKGROUND

Silicon-on-insulator is the process of fabricating silicon baseddevices, such as complementary metal oxide semiconductor (CMOS) fieldeffect transistors (FET) on top of a layer of electrically insulatingmaterial, such as an oxide. The layer of oxide is on top of a bulksilicon substrate in an integrated circuit (IC) chip and acts as anelectrical barrier between the devices (e.g., FETs) and the bulksilicon. The layer of oxide greatly reduces electrical leakage from thedevices, but also greatly reduces heat flow away from these devices.Accumulation of heat within a device, such as a FET, can reduce theperformance and/or useful lifetime of the device.

Heat generation is a limiting factor to improving device operation inmany technologies. For example, in radio frequency (RF) CMOS, switchperformance is severely limited by the heat generated by the switch athigh frequency. RF switches can use 200-300 mW of power, while an RFamplifier can use up to 3 W of power. This large amount of current flowover a relatively small region can result in heating of the devices upto 200° C. in the case of an RF amplifier. These elevated temperaturescan significantly change the characteristics of the devices, as well asdegrade the integrity of its construction materials. Since many of thesedevices are now built on SOI, the primary path for drawing heat awayfrom the devices is through the electrical contacts formed over thedevices. Further amplifying this problem is the desire to remove orreduce the number of electrical contacts in order to lower thecapacitance of the devices, which will increase the need to dissipateheat because the electrical contacts do provide a path for the heat toescape. The RF parts affected by this issue are largely in cellulartelephones.

Similar heat-related issues are present in the bipolar junctiontransistor (BJT) devices that are commonly used in radar and collisionavoidance. SiGe-based BJT devices are driving toward increased operatingfrequencies of up to 300 GHz. As this frequency increases, the trappedresidual heat plays a more prevalent role in degrading deviceperformance. Passive structures, such as resistors, are also negativelyaffected by excess heat, which can affect the temperature coefficient ofresistance.

SUMMARY

In a first aspect of the invention, a method of manufacturing asemiconductor structure includes forming an isolation layer on anelectrically conductive feature of an integrated circuit device, whereinthe isolation layer is electrically insulating and thermally conducting.The method also includes forming an electrically conductive layer on theisolation layer. The method additionally includes forming a plurality ofnanowire structures on a surface of the electrically conductive layer.

In another aspect of the invention, a method of manufacturing asemiconductor structure includes forming an isolation layer on anelectrically conductive feature of an integrated circuit device. Themethod includes forming an electrically conductive layer on theisolation layer. The method also includes forming a plurality ofnanowire structures on a surface of the electrically conductive layer.The isolation layer is formed to electrically isolate the electricallyconductive feature from the electrically conductive layer. The pluralityof nanowire structures are formed of a high thermal conductivitymaterial that provides a heat path away from the electrically conductivefeature.

In yet another aspect of the invention, a semiconductor structureincludes: an isolation layer on an electrically conductive feature of anintegrated circuit device; an electrically conductive layer on theisolation layer; and a plurality of nanowire structures on a surface ofthe electrically conductive layer. The isolation layer electricallyisolates the electrically conductive feature from the electricallyconductive layer. The plurality of nanowire structures are composed of ahigh thermal conductivity material that provides a heat path away fromthe electrically conductive feature.

In another aspect of the invention, a design structure tangibly embodiedin a machine readable storage medium for designing, manufacturing, ortesting an integrated circuit is provided. The design structurecomprises the structures of the present invention. In furtherembodiments, a hardware description language (HDL) design structureencoded on a machine-readable data storage medium comprises elementsthat when processed in a computer-aided design system generates amachine-executable representation of a semiconductor structure withnanowires which comprises the structures of the present invention. Instill further embodiments, a method in a computer-aided design system isprovided for generating a functional design model of the semiconductorstructure with nanowires. The method comprises generating a functionalrepresentation of the structural elements of the semiconductor structurewith nanowires.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIGS. 1-13 show processing steps and structures in accordance withaspects of the invention;

FIG. 14 shows data of a thermal model in accordance with aspects of theinvention; and

FIG. 15 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test.

DETAILED DESCRIPTION

The invention relates to integrated circuits and, more particularly, tomethods and systems for dissipating heat in integrated circuit devices.According to aspects of the invention, nanowire structures are formed toproduce an electrically isolated but thermally conductive path for heatto diffuse away from a device. By placing nanowires on and near devices,the nanowires provide a path for heat dissipation and/or heat transportfrom a source to a sink, and drastically cool the device, which improvesdevice performance. In embodiments, the nanowires comprise zinc oxide(ZnO), which provides the benefit that the nanowires are easily formedwith high selectivity via an electrochemical hydrothermal bath. Inaddition, ZnO has a high thermal conductivity and is a cost-effective,environmentally friendly, and readily available material. Includingthese nanowire heat fins in devices as described herein provides forfurther optimization of devices, such as reducing the number of contactsto lower the capacitance of RF devices.

Implementations of the invention include providing an electricallyisolated but thermally conductive path for heat to diffuse away from thedevice. Such heat removal allows the device to operate with increasedperformance and reduces the likelihood of heat-related materialsdegradation. Embodiments include growing ZnO nanowires on top of aconductive material (e.g., silicide) that is deposited on top of anelectrical isolation layer above the device. The pads and wiring used inthe nanowire deposition may also be used for heat conduction from thenanowire arrays to the metal pads.

The semiconductor structures of the present invention can bemanufactured in a number of ways using a number of different tools. Ingeneral, and unless otherwise noted herein, the methodologies and toolsare used to form structures with dimensions in the micrometer scale. Themethodologies, i.e., technologies, employed to manufacture thesemiconductor structures of the present invention have been adopted fromintegrated circuit (IC) technology. For example, the structures of thepresent invention are built on wafers and are realized in films ofmaterial patterned by photolithographic processes on the top of a wafer.In particular, the fabrication of the semiconductor structures of thepresent invention may use three basic building blocks: (i) deposition ofthin films of material on a substrate, (ii) applying a patterned mask ontop of the films by photolithographic imaging, and (iii) etching thefilms selectively to the mask.

FIGS. 1-13 show processing steps and respective structures in accordancewith aspects of the invention. Specifically, FIG. 1 shows an exemplarySOI wafer 10 employed as an intermediate structure in implementations ofthe invention. The SOI wafer 10 has a bulk semiconductor substrate 15,which is typically a bulk silicon substrate, a buried insulator layer 20formed on the substrate 15, and a semiconductor layer 25, which istypically a silicon layer formed on the buried insulator layer 20. TheSOI wafer 10 may be fabricated using techniques understood by thoseskilled in the art. For example, the SOI wafer 10 may be formed byconventional processes including, but not limited to, oxygenimplantation (e.g., SIMOX), wafer bonding, etc.

The constituent materials of the SOI wafer 10 may be selected based onthe desired end use application of the semiconductor device. Forexample, the substrate 15 may be composed of any suitable materialincluding, but not limited to, Si, SiGe, SiGeC, SiC, GE alloys, GaAs,InAs, InP, and other III/V or II/VI compound semiconductors. The buriedinsulator layer 20 may be composed of oxide, such as SiO₂, and may bereferred to as a buried oxide (BOX) layer 20. Moreover, although the SOIwafer is referred to as “silicon on insulator,” the semiconductor layer25 is not limited to silicon. Instead, the semiconductor layer 25 may becomprised of various semiconductor materials, such as, for example, Si,SiGe, SiC, SiGeC, etc.

In embodiments, the SOI wafer 10 has a thickness of about 700 μm, withthe BOX layer 20 having a thickness in a range of about 0.1 μm to about2 μm, and the semiconductor layer 25 having a thickness in a range ofabout 0.1 μm to about 0.2 μm. However, the invention is not limited tothese dimensions, and the various portions of the SOI wafer may have anydesired thicknesses based upon the intended use of the finalsemiconductor device.

Still referring to FIG. 1, shallow trench isolation (STI) structures 30may be formed in the wafer 10. The STI 30 may be conventional shallowtrench isolation structures formed using conventional semiconductorfabrication processes such as photolithographic masking and etching. Forexample, the STIs 30 may be formed by arranging a photoresist materialon the semiconductor layer 25, exposing and developing the photoresist,etching an STI trench in the semiconductor layer 25 through thepatterned photoresist (e.g., using a reactive ion etch (RIE) process),stripping the photoresist, filling the trench with an STI material(e.g., SiO₂), and planarizing the top surface of the structure (e.g.,via chemical mechanical polish (CMP)). The STI 30 locally replaces aportion of the semiconductor layer 25. The remaining portion of thesemiconductor layer 25 that is surrounded by the STI 30 is referred toas an island 35.

With continued reference to FIG. 1, a FET 80 is formed in the wafer 10using conventional semiconductor materials and manufacturing processes.The FET 80 may be of any desired configuration, and may be formed usingconventional CMOS fabrication techniques and materials. For example, theFET 80 may be formed by first forming a gate dielectric 81 on the uppersurface of the wafer 10 including the top surface of the island 35,forming a gate conductor 82 on the gate dielectric 81, and patterningthe gate conductor 82 and the gate dielectric 81 to form a gate 83 onthe island 35. The gate dielectric 81 may be any suitable material,including, for example, high-k dielectrics such as hafnium-basedmaterials. The gate conductor 82 can be any suitable material, such asdoped polysilicon, metal, or a combination of layers thereof. Sidewallspacers 84 may be formed on the gate conductor 82, e.g., using CVD ofnitride or oxide and RIE. Source/drain regions 85 a/85 b may be formedin the island 35 by performing an ion implantation of appropriate typeimpurities.

As shown in FIG. 2, a block 90 is formed on the drain region 85 b. Theblock 90 may be composed of any suitable material that prevents theformation of silicide on the drain region 85 b in subsequent processingsteps. For example, the block 90 may comprise nitride. The block 90 maybe formed using conventional CMOS processing techniques, such asdepositing a blanket layer of nitride on the entire wafer, and maskingand etching the nitride to shape the block 90.

Still referring to FIG. 2, after forming the block 90, silicide 100 isformed on silicon-containing surfaces that are unmasked by the block 90,e.g., on the source region 85 a and the gate conductor 82 of the FET 80.The silicide 100 may be formed using conventional CMOS processingtechniques, such as: sputtering a layer of metal onto the top surface ofthe wafer; annealing the wafer to react the metal with silicon in placeswhere the metal contacts silicon; and stripping any unreacted metal.

FIG. 3 shows forming a barrier layer 110 on the structure, including onblock 90. The barrier layer 110 may be formed using conventionalmaterials and processes, such as CVD of nitride. In embodiments, thebarrier layer 110 comprises the same material as the block 90.

FIG. 4 shows removing portions of the barrier layer 110 and the block 90to expose the upper surface of the drain region 85 b. The portions ofthe barrier layer 110 and block 90 may be removed using standardpatterning, such as photolithographic masking and etching (e.g., RIE).

FIG. 5 shows forming an isolation layer 120 on the drain region 85 b,and forming an electrical conducting layer 130 on the isolation layer120 in accordance with aspects of the invention. In embodiments, theisolation layer 120 is composed of a material that has a low electricalconductivity (e.g., is a dielectric material) and a high thermalconductivity. As used herein, a high thermal conductivity material is amaterial that has a thermal conductivity that is substantially greaterthan (e.g., at least ten times) the thermal conductivity of the materialof the BOX layer 20. In embodiments, the BOX layer 20 is composed ofSiO₂ that has a nominal thermal conductivity of about 1 W/(m·K), and theisolation layer 120 is composed of Al₂O₃ (referred to as alumina oraluminum oxide), which has a nominal thermal conductivity of about 30W/(m·K). The isolation layer 120 is not limited to these materials, andany suitable low electrical conductivity and high thermal conductivitymaterial may be used. The isolation layer 120 may be formed usingstandard processing techniques, such as CVD or plasma enhanced CVD(PECVD) and photolithographic patterning. The isolation layer 120 is notlimited to alumina, and other materials may be used, including apolymorphic ceramic such as boron nitride (BN), etc. The isolation layermay also comprise other ceramic materials, such as zirconia (ZrO₂) andaluminum nitride (AlN).

With continued reference to FIG. 5, the conducting layer 130 is formedon the isolation layer 120. The conducting layer 130 may be composed of,for example, silicide, sputtered metal, or the like. When composed ofsilicide, the conducting layer 130 may be formed in the manner describedherein, e.g., depositing polysilicon, patterning the polysilicon,sputtering metal, reacting the metal with the polysilicon, and removingunreacted metal. In aspects, the conducting layer 130 constitutes anelectrically conductive layer formed on the isolation layer 120 that, inturn, is formed on an electrically conductive feature of the integratedcircuit device, i.e., the drain region 85 b. The invention is notlimited to use with a drain region, however. Instead, as describedherein, the electrically conductive feature is a semiconductor device,such a field effect transistor or bipolar junction transistor or adiffusion resistor, which can generate heat during operation to theextent that the generated heat degrades the performance of the deviceitself, or of neighboring devices, or physically damages the constituentelements of the structure in which the devices are fabricated.

FIG. 6 shows forming high thermal conductivity nanowires 140 on theconducting layer 130 in accordance with aspects of the invention. Thenanowires 140 are vertically oriented columnar structures that extendupward from the surface of the conducting layer 130. The nanowires 140are composed of high thermal conductivity material and function as heatexchanger fins that enhance the rate of heat transfer away from the FET80. In this manner, the nanowires 140 provide a heat path to dissipateheat and/or transport heat away from the electrically conductive featureon which they are formed.

In embodiments, the nanowires 140 comprise zinc oxide (ZnO) and areformed with high selectivity using an electrochemical hydrothermal bath.ZnO is a semiconductor material having a high thermal conductivity ofabout 135 W/(m·K). An exemplary process for forming the nanowires 140includes providing a solution comprising a 1:1 mixture of 0.025 M zincnitrate hexahydrate (Zn(NO₃)₂.6H2O) and 0.025 M hexamethylenetetramine(HMTA, C₆H₂N₄) in deionized water. The solution is stirred and heated toabout 90° C. The wafer is suspended in the solution at this temperaturewith the growth surface (i.e., the exposed conducting layer 130) facingdownward. A first electrode of an external voltage application circuitis connected through wiring in the wafer 10 to the conducting layer 130,and a second electrode of the external voltage application circuit issuspended in the solution. The external voltage application circuitapplies a potential of about 1 V to 5 V between the first electrode andthe second electrode while the growth surface is submerged in thesolution. Under these conditions, the nanowires 140 grow as spaced apartcolumnar structures on the growth surface via an electrochemicaldeposition process. The invention is not limited to forming thenanowires 140 using an electrochemical deposition process, and insteadthe nanowires 140 may be formed using any suitable formation process.

The voltage and amount of time applying the voltage in solution may beused to control the height and width of the nanowires 140. In oneexample, each one of the nanowires 140 is grown to a nominal height “h”of about 1700 nm and a nominal width “w” of about 240 nm using a voltageof 2.5 V and a growth time of 60 minutes. In one example, each one ofthe nanowires 140 is grown to a nominal height of about 3000 nm and anominal width of about 640 nm using a voltage of 2.5 V and a growth timeof 120 minutes. Height of the nanowires 140 is measured as the extent ofgrowth outward from the growth surface, e.g., the exposed surface of theconducting layer 130. As used herein, nanowire and nanowire structurerefer to a columnar structure having a sub-micron width. The inventionis not limited to these values, and one or more of the parameters of thegrowth process (e.g., constituents of the solution, temperature, voltagepotential, growth time, etc.) may be tailored to achieve a desirednanowire structure according to aspects of the invention.

FIG. 7 shows the structure after forming an insulator layer 200 on thewafer 10 and electrical contacts 205 in the insulator layer 200. Theinsulator layer 200 and electrical contacts 205 may be formed usingconventional CMOS processes and materials. For example, the insulatorlayer 200 may comprise any conventional dielectric material, such as,for example, silicon dioxide (SiO₂), borophosphosilicate glass (BPSG),etc. The electrical contacts 205 may be formed by forming a photomask onthe insulator layer 200, etching holes in the insulator layer 200 andbarrier layer 110 through the photomask, stripping the photomask,filling the holes with an electrically conductive material (e.g.,tungsten, copper, etc.) using CVD, and planarizing the top surface ofthe wafer 10 using CMP. One or more additional insulator layers 210 andmetal layers 215 may be formed on the insulator layer 200 and electricalcontacts 205 to provide electrical connectivity to the source and drainregions of the FET 80.

FIG. 8 shows a plan view of an RF device including a FET 80 formed inaccordance with the process described with respect to FIGS. 1-7. FIG. 7is a cross section view taken along line VII-VII of FIG. 8. As shown inFIG. 8, the source region 85 a and drain region 85 b extend for length“L” on opposite sides of gate 83. Gate contact 150 may be placed incontact with each gate 83. In embodiments, the nanowires 140(collectively shown as a shaded area) are formed on a first portion ofthe drain region 85 b, and contacts 205′ are formed on a second portionof the drain region 85 b. Similarly, contacts 205 are formed on a firstportion of the source region 85 a, and nanowires 140′ (collectivelyshown as a shaded area) are formed on a second portion of the sourceregion 85 a. In this manner each one of the source region 85 a and drainregion 85 b is provided with its own electrical contacts and its ownnanowire structures.

In aspects, the nanowires 140′ on the source region 85 a and thenanowires 140 on the drain region 85 b are formed simultaneously. Forexample, a conducting layer similar to conducting layer 130 may beformed on the second portion of source region 85 a at the same time andin the same manner of formation as conducting layer 130 usingappropriate mask patterns. In this manner, nanowires 140 and 140′ aregrown at the same time using the electrochemical deposition processdescribed herein. Similarly, the contacts 205 and 205′ may be formedsimultaneously using the processes described with respect to FIG. 7 andappropriate mask patterns.

FIGS. 9-11 depict exemplary arrangements for providing an electricallyconductive path to the growth surface of a wafer for applying thevoltage when growing the nanowires in accordance with aspects of theinvention. FIG. 9 shows a schematic diagram that includes a contact pad305 formed on the wafer (e.g., wafer 10), the contact pad 305 beingstructured and arranged to physically contact the first electrode of theexternal voltage application circuit used in the nanowireelectrochemical deposition process. As shown in FIG. 9, electricallyconductive wiring 310 (e.g., wires, vias, interconnects, etc.) is formedin the structure of the wafer between the contact pad 305 and pluralgrowth surfaces 315 a-n (e.g., plural discrete instances of conductinglayers 130). In this manner, the voltage potential may be applied to thegrowth surfaces to facilitate growing the nanowire structures. Inembodiments, the growth surfaces are placed where the heat conductionand/or dissipation is desired, e.g., as described with respect to FIG.8.

FIG. 10 shows a plan view of a wafer in which growth surfaces areconnected to a substrate contact in accordance with aspects of theinvention. The structure of FIG. 10 includes a plurality of FETs 80including a plurality of gates 83 and a plurality of source/drainregions 85 a/85 b, e.g., in an RF device layout similar to that shown inFIG. 8 before the contacts and nanowires are formed. In embodiments,each one of a plurality of growth surfaces, i.e., conducting layers 130a-n, is electrically connected to a substrate contact 350 by a wiringpaths 353 a-n. Each wiring path 353 a-n may include a breakable element355 a-n, such as a high resistance link or e-fuse. The substrate contact350 is connected to a contact pad, such as contact pad 305 described inFIG. 9, for providing the voltage potential across the conducting layers130 a-n for growing the nanowire structures thereon. After forming thenanowire structures on the conducting layers 130 a-n, the breakableelements 355 a-n may be physically broken to create an electricaldiscontinuity between the conducting layers 130 a-n and the substratecontact 350. For example, when the breakable elements 355 a-n comprisee-fuses, the breakable elements 355 a-n may be broken by applying asufficiently high voltage to blow the e-fuse (e.g., a programmingvoltage).

FIG. 11 shows an embodiment of the structure of FIG. 5 connected to acontact pad in a manner similar to that described with respect to FIG.10. As depicted in FIG. 11, the conducting layer 130 is electricallyconnected to a substrate contact 350 via wiring path 353 (shown indashed lines) and breakable element 355. In aspects, the substratecontact 350 is an electrically conductive through silicon via thatextends from a front side 360 of the wafer 10 to a back side 365 of thewafer 10, and contacting a contact pad 370 (e.g., similar to contact pad305) formed on the back side 365. In this manner, contact pad 370 on theback side 365 of the wafer 10 may be used as a physical contact locationfor connecting an electrode that provides the voltage to conductinglayer 130 during the nanowire growth process.

FIG. 12 depicts an implementation of nanowire structures on a bipolarjunction transistor (BJT) in accordance with aspects of the invention.As shown in FIG. 12, a BJT 400 may comprise an n-type semiconductormaterial collector 405 formed in a substrate 410, a p-type semiconductormaterial base 415 formed over the collector 405, and an n-typesemiconductor material emitter 420 formed over the base 415. Thesubstrate 410 may comprise doped silicon and the base 415 may compriseSiGe, for example. STI structures 425 may be formed in the substrate 410around the collector 405. In embodiments, an isolation layer 120″ and aconducting layer 130″ are formed on portions of the base 415, e.g., in amanner similar to that described with respect to FIG. 5. Subsequently,nanowire structures 140″ are formed on the conducting layer 130″, e.g.,in a manner similar to that described with respect to FIG. 6. Aninsulator layer 200″ and electrical contacts 205″ may be formed over theBJT 400, e.g., in a manner similar to that described with respect toFIG. 7. Depending upon the desired configuration of the BJT as thefunctional circuit of interest, the nanowires can be grown on one of thecollector contacts for maximum heat dissipation. This would be useful ina “common base” BJT configuration, example.

FIG. 13 depicts an implementation of nanowire structures on a passivedevice in accordance with aspects of the invention. As shown in FIG. 13,passive device may comprise a resistor 505 formed on a BOX layer 20′″ ona substrate 15′″. In embodiments, an isolation layer 120′″ and aconducting layer 130′″ are formed on portions of the resistor 505, e.g.,in a manner similar to that described with respect to FIG. 5.Subsequently, nanowire structures 140′″ are formed on the conductinglayer 130′″, e.g., in a manner similar to that described with respect toFIG. 6. An insulator layer 200″′ and electrical contacts 205′″ may beformed over the resistor 505, e.g., in a manner similar to thatdescribed with respect to FIG. 7.

FIG. 14 shows a plot 600 of data illustrating device temperature (° C.)versus ZnO stud density and conductivity (W/cm²) for three differentstud densities (1×, 2×, 4×) in accordance with aspects of the invention.Stud density relates to nanowire structures 130, where a 1× stud densitycorresponds to 250 nm×250 nm. The data was obtained using a thermalmodel of an SOI device similar to that described with respect to FIGS.1-7. The thermal modeling shows device temperature improvement on theorder of 50-60 degrees using implementations of the invention.

FIG. 15 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test. FIG. 15 shows a block diagram of anexemplary design flow 900 used for example, in semiconductor IC logicdesign, simulation, test, layout, and manufacture. Design flow 900includes processes, machines and/or mechanisms for processing designstructures or devices to generate logically or otherwise functionallyequivalent representations of the design structures and/or devicesdescribed above and shown in FIGS. 1-13. The design structures processedand/or generated by design flow 900 may be encoded on machine-readabletransmission or storage media to include data and/or instructions thatwhen executed or otherwise processed on a data processing systemgenerate a logically, structurally, mechanically, or otherwisefunctionally equivalent representation of hardware components, circuits,devices, or systems. Machines include, but are not limited to, anymachine used in an IC design process, such as designing, manufacturing,or simulating a circuit, component, device, or system. For example,machines may include: lithography machines, machines and/or equipmentfor generating masks (e.g. e-beam writers), computers or equipment forsimulating design structures, any apparatus used in the manufacturing ortest process, or any machines for programming functionally equivalentrepresentations of the design structures into any medium (e.g. a machinefor programming a programmable gate array).

Design flow 900 may vary depending on the type of representation beingdesigned. For example, a design flow 900 for building an applicationspecific IC (ASIC) may differ from a design flow 900 for designing astandard component or from a design flow 900 for instantiating thedesign into a programmable array, for example a programmable gate array(PGA) or a field programmable gate array (FPGA) offered by Altera® Inc.or Xilinx® Inc.

FIG. 15 illustrates multiple such design structures including an inputdesign structure 920 that is preferably processed by a design process910. Design structure 920 may be a logical simulation design structuregenerated and processed by design process 910 to produce a logicallyequivalent functional representation of a hardware device. Designstructure 920 may also or alternatively comprise data and/or programinstructions that when processed by design process 910, generate afunctional representation of the physical structure of a hardwaredevice. Whether representing functional and/or structural designfeatures, design structure 920 may be generated using electroniccomputer-aided design (ECAD) such as implemented by a coredeveloper/designer. When encoded on a machine-readable datatransmission, gate array, or storage medium, design structure 920 may beaccessed and processed by one or more hardware and/or software moduleswithin design process 910 to simulate or otherwise functionallyrepresent an electronic component, circuit, electronic or logic module,apparatus, device, or system such as those shown in FIGS. 1-13. As such,design structure 920 may comprise files or other data structuresincluding human and/or machine-readable source code, compiledstructures, and computer-executable code structures that when processedby a design or simulation data processing system, functionally simulateor otherwise represent circuits or other levels of hardware logicdesign. Such data structures may include hardware-description language(HDL) design entities or other data structures conforming to and/orcompatible with lower-level HDL design languages such as Verilog andVHDL, and/or higher level design languages such as C or C++.

Design process 910 preferably employs and incorporates hardware and/orsoftware modules for synthesizing, translating, or otherwise processinga design/simulation functional equivalent of the components, circuits,devices, or logic structures shown in FIGS. 1-13 to generate a netlist980 which may contain design structures such as design structure 920.Netlist 980 may comprise, for example, compiled or otherwise processeddata structures representing a list of wires, discrete components, logicgates, control circuits, I/O devices, models, etc. that describes theconnections to other elements and circuits in an integrated circuitdesign. Netlist 980 may be synthesized using an iterative process inwhich netlist 980 is resynthesized one or more times depending on designspecifications and parameters for the device. As with other designstructure types described herein, netlist 980 may be recorded on amachine-readable data storage medium or programmed into a programmablegate array. The medium may be a non-volatile storage medium such as amagnetic or optical disk drive, a programmable gate array, a compactflash, or other flash memory. Additionally, or in the alternative, themedium may be a system or cache memory, buffer space, or electrically oroptically conductive devices and materials on which data packets may betransmitted and intermediately stored via the Internet, or othernetworking suitable means.

Design process 910 may include hardware and software modules forprocessing a variety of input data structure types including netlist980. Such data structure types may reside, for example, within libraryelements 930 and include a set of commonly used elements, circuits, anddevices, including models, layouts, and symbolic representations, for agiven manufacturing technology (e.g., different technology nodes, 32 nm,45 nm, 90 nm, etc.). The data structure types may further include designspecifications 940, characterization data 950, verification data 960,design rules 970, and test data files 985 which may include input testpatterns, output test results, and other testing information. Designprocess 910 may further include, for example, standard mechanical designprocesses such as stress analysis, thermal analysis, mechanical eventsimulation, process simulation for operations such as casting, molding,and die press forming, etc. One of ordinary skill in the art ofmechanical design can appreciate the extent of possible mechanicaldesign tools and applications used in design process 910 withoutdeviating from the scope and spirit of the invention. Design process 910may also include modules for performing standard circuit designprocesses such as timing analysis, verification, design rule checking,place and route operations, etc.

Design process 910 employs and incorporates logic and physical designtools such as HDL compilers and simulation model build tools to processdesign structure 920 together with some or all of the depictedsupporting data structures along with any additional mechanical designor data (if applicable), to generate a second design structure 990.

Design structure 990 resides on a storage medium or programmable gatearray in a data format used for the exchange of data of mechanicaldevices and structures (e.g. information stored in a IGES, DXF,Parasolid XT, JT, DRG, or any other suitable format for storing orrendering such mechanical design structures). Similar to designstructure 920, design structure 990 preferably comprises one or morefiles, data structures, or other computer-encoded data or instructionsthat reside on transmission or data storage media and that whenprocessed by an ECAD system generate a logically or otherwisefunctionally equivalent form of one or more of the embodiments of theinvention shown in FIGS. 1-13. In one embodiment, design structure 990may comprise a compiled, executable HDL simulation model thatfunctionally simulates the devices shown in FIGS. 1-13.

Design structure 990 may also employ a data format used for the exchangeof layout data of integrated circuits and/or symbolic data format (e.g.information stored in a GDSII (GDS2), GL1, OASIS, map files, or anyother suitable format for storing such design data structures). Designstructure 990 may comprise information such as, for example, symbolicdata, map files, test data files, design content files, manufacturingdata, layout parameters, wires, levels of metal, vias, shapes, data forrouting through the manufacturing line, and any other data required by amanufacturer or other designer/developer to produce a device orstructure as described above and shown in FIGS. 1-13. Design structure990 may then proceed to a stage 995 where, for example, design structure990: proceeds to tape-out, is released to manufacturing, is released toa mask house, is sent to another design house, is sent back to thecustomer, etc.

The methods as described above are used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed:
 1. A bipolar junction transistor comprising: acollector formed in a substrate; a base formed on the substrate and overthe collector; and an emitter formed on and over the base; an isolationlayer formed on and over a first portion of the base; an electricallyconductive layer formed on and over the isolation layer; a plurality ofnanowire structures formed on a surface of the electrically conductivelayer above the first portion of the base, and a contact in electricalcontact with the collector and formed over a portion of the substrateadjacent to a second portion of the base, wherein the second portion ofthe base is located between the first portion of the base, which thenanowire structures are formed on, and the portion of the substratewhich the collector electrical contact is formed over.
 2. The bipolarjunction transistor of claim 1, wherein the isolation layer comprises ahigh thermal conductivity material that electrically isolates the basefrom the electrically conductive layer.
 3. The bipolar junctiontransistor of claim 1, wherein the isolation layer comprises polymorphicceramic.
 4. The bipolar junction transistor of claim 1, wherein theisolation layer comprises one of alumina (Al₂O₃), boron nitride (BN),zirconia (ZrO₂), and aluminum nitride (AlN).
 5. The bipolar junctiontransistor of claim 1, wherein the electrically conductive layercomprises silicide on the isolation layer.
 6. The bipolar junctiontransistor of claim 1, wherein the plurality of nanowire structurescomprises a plurality of spaced apart columnar structures each having asub-micron width.
 7. The bipolar junction transistor of claim 1, furthercomprising: an insulator layer on and around the plurality of nanowirestructures; and an electrical contact of the bipolar junction transistorin the insulator layer.
 8. The bipolar junction transistor of claim 1,wherein: the collector and the emitter each comprise n-typesemiconductor material; and the base comprises p-type semiconductormaterial.
 9. The bipolar junction transistor of claim 8, wherein thesubstrate comprises doped silicon.
 10. The bipolar junction transistorof claim 1, further comprising shallow trench isolation structuresformed in the substrate around the collector.
 11. The bipolar junctiontransistor of claim 1, wherein the collector electrical contact isformed over a silicide layer which is located between the collectorelectrical contact and the portion of the substrate which the collectorelectrical contact is formed over.
 12. The bipolar junction transistorof claim 12, further comprising an insulator layer formed over thenanowire structures, the electrically conductive layer and the collectorelectrical contact.
 13. The bipolar junction transistor of claim 12,wherein the collector electrical contact extends through the insulatorlayer from an upper surface of the insulator layer to an upper surfaceof the silicide layer.
 14. The bipolar junction transistor of claim 13,wherein the silicide layer is adjacent to and spaced apart from thebase.